Will the Universe continue to expand?
If the mean density of the Universe is less than a certain critical value, the rate expansion should tend to remain steady and the Universe would expand forever.
If the density is greater than the critical value, the expansion will eventually slow down and cease, followed by a contraction phase. According to the Oscillating Universe Theory, the Universe expands and contracts in a cyclic manner repeatedly.
Is the volume of matter so far detected in the Universe likely to exceed the critical value required to substantiate the Oscillating Universe Theory?
The volume of matter detected so far is below the critical value. However, there are various types of matter in the Universe about which we have incomplete knowledge e.g., inter-galactic matter and “invisible” matter.
What is meant by inter-galactic matter?
Inter-galactic matter refers to the rarefied matter that exists in the space between the galaxies. Its existence has not been proved by direct observation but indirectly by interfaces.
What are the basic constituents of the “matter” in the Universe?
Matter refers to material objects. The smallest unit of matter that can exist independently as a chemical element is the atom. Groups of atoms combined together are known as molecules. The atom itself consists of a core called the “nucleus” surrounded by an outer shell containing particles called electrons.